US2374090A - Apparatus for intensifying speech in the human vocal cavities - Google Patents

Description

April 17, 1945. D N} R FRENCH 2,374,090 APPARATUS FOR INTENSIFYING SPEECH IN THE HUMAN VOCAL CAVITIES Filed Dec. 11, 1943v ,8 l7 I0 1 I la NORMAL SPEECH (PLUS REINFORCED SPEECH I EINFORCED SPEECH AMPLITUDE AMBIENT NIOISE n SP EAKER FREQUENCY WV'ENTOR M R FRENCH ATTORNEY Patented Apr. 17., 1945 APPARATUS FOR INTENSIFYING SPEECH IN 'THE HUMAN VOCAL 'CAVITIES Norman E. French, Pleasantville, N. Y., assignor.

to Bell Telephone Laboratories, Incorporated, New link, N. Y., a corporation of New York Application December 11, 1943, Serial No. 513,857

, 12 mm. This invention relates to a .nethod of and apparatus for enabling a speaker to deliver by his own voice speech vibration having amplitudes whichv are larger than the amplitudes of the speech vibrations that he could produce by his vocal efiorts alone.

When a speaker is immersed in ambient noise of a high level, he usually finds it diillcult to raise the level of his voice above that of the noise near his lips, without tending to strain his voice.

This means that such unfavorable speech-tonoise ratio exists near the speaker's lips that a listener even close to the-speaker would have difflculty in comprehending the speech. The same diillculty would exist; when the listener moved away from the speaker; and, when the speech was reproduced at a distance from the speaker by means of a public address system or the like embodying a microphone positioned near the speaker's lips. This follows because such system a would tend to attenuate" or amplify speech and noise substantially to the same extent leaving substantially unchanged the speech-to-noise ratio of the transmitted speech and noise.

The present invention is concerned with in-.

creasing the level of the speech vibrations delivered by the human voice, and thereby the speechto-noise ratio in proximity of the speaker's lips.

The present invention contemplates an arrangement for mechanically producing sound vibrations of certain frequencies and amplitudes and introducing them into the vocal cavities of a speaker, together with the sound vibrations produced naturally by the speaker and thereby sub-- stantially increasing the amplitudes of the speech vibrations delivered by the voice of the speaker.

The main object of the invention i to increase the amplitudes of the frequencies in a speech spectrum delivered by the voice of a speaker.

Another object is to increase the value of the speech-to-noise ratio of speech transmitted directly through an air transmission'medium which immerses both the speaker and listener in ambient noise. v 1

A further object is to increase the value of the speech-tomoise ratio of speech transmitted over a public address system arranged such that both the speaker and microphone pick-up are immersed in ambient noise.

As a talker in noisy surroundings raises his voice to make himself heard, he experiences difficulty because the higher voice frequencies which contribute greatly'to intelligibility and which are .relatively weak may still be too close to the noise a level. evgn when the take; is shouting, Exp'efl- 5 A feature of the invention is that the mechani- "roughly the same amplitude.

The present invention aims to take advantage of this fact by providing for selectively building up the higher frequency energy of speech waves to enable the speech to be understood through noise In a particular case where the noise has a given type of frequency energy characteristic the invention provides for predistorting the emitted voice waves to better enable them to override the voice by givingthem an, improved frequency-by-irequency speech-tosnoise ratio over the band. a

In a specific embodiment, the invention comprises in sequence one or more electroacoustic transducers applied to the skin in the region of the throat of a speaker, a low-pass filter, an amplifier, a harmonic producer, a high-pass filter, a network for controlling the amplitudes of individual'frequencies, and an electrcacoustic converter whose output is introduced into the vocal cavities of the speaker.

In operation, the sound vibrations at the surface of the skin in the region of the throat of harmonic currents are then translated into other sound vibrations whose frequencies and amplitudes correspond substantially to those of the harmonic currents. These sound vibrations are introduced into the vocal cavities of the speaker to be molded by the cavities of his throat, mouth and nasal passages into speech, together with the sound vibrations produced naturally in the speakers throat. Thus, the amplitudes of the speech vibrations delivered by the speaker's voice are substantially increased with reference to the level of the ambient noise, without requiring a noticeable increase in the vocal efforts of the speaker.

tain range of audible frequencies.

cally produced sound vibrations may be introduced into the vocal cavities of the speaker either through the mouth of the speaker, or through the skin in the region of the throat of the speaker. Another feature concerns compensation for the vocal output of the speaker as he tends to relax his vocal efforts.

The invention will be readily understood from the following description taken together with'the accompanying drawing in which:

Fig. 1 is a schematic circuit illustrating the speciflc embodiment of the invention;

Fig. 2 is a family of curves illustrating action with such amplitude versus frequency characteristic that the combined speech vibrations delivered by the speakers voice are provided with a favorable value of speech-to-noise ratio, with reference to, the ambient noise spectrum in which the speaker may be immersed. Compensation for .-the tendency of the speaker to relax his vocal eiforts is provided by the automatic gain control brations'of fundamental frequency and harmonics thereof, as the speaker produces them, and to translate such vibrations into electric currents of fundamental and harmonic frequencies corresponding to those of the sound vibrations. The microphone as shown comprises a pair of electroacoustic converters connected in series. In accordance with the familiar practice, these converters may also be connected in parallel and may comprise one or more converters as desired.

These harmonic currents are supplied to a lowpass filter H which passes the fundamental current but suppresses the harmonicLcurrents. The fundamental current is amplified in amplifier l2 embodying suitable automatic gain control, and thereafter impressed on a harmonic producer i8 whose output includes both the fundamental current and harmonics thereof extending over a cer- This range may comprise the entire audible range or a desired portion of it, and may correspond in toto or in part to the frequencies of the sound vibrations produced in the human throat as previously mentioned.

The harmonic currents are supplied to a highpass filter 14 which passes the harmonic currents but suppresses the fundamental. The harmonic currents are then supplied to a network it which relatively varies the amplitudes of individual harmonics. For example, the range of harmonic currents appearing in the output of the network l5 may be preshaped with amplitudes of predetermined. relative magnitudes with reference to the spectrum of a particular ambient noise.

The latter harmonic currents are then supplied over a pair of leads l8, IE to an electroacoustic converter I1, and thereby translated into sound vibrations whose frequencies and amplitudes correspond substantially to the frequencies and amplitudes, respectively, of the harmonic currents. These sound vibrations are introduced via a hollow tube l8 into the vocal cavities of the speaker,

such as the resonant chambers of the mouth, throat and nasal passages, for molding into audible sounds in the same manner as the molding of normal speech vibrations.

In the operation of Fig. l, the sound vibrations produced in the speaker's throat are introduced into his vocal cavities for molding intoaudible sounds which are delivered by the speaker's voice in' the familiar manner. The mechanically produced vibrations introduced into the vocal cavities in the manner pointed out .above are com.-

bined with the naturally produced vibrations so of amplifier l2 operating in the familiar manner. The combination of low-pass filter, harmonic producer and high-pass filter eliminates the tendency of the loop to sing. I

Fig, 2 shows the value of the speech-to-noise ratio of normal speech produced in an assumed ambient noise spectrum; the value of the speechto-noise ratio of the reinforced speech in the same noise spectrum; and the value of the speechto-noise ratio of the combined normal and reinforced speech in the same noise spectrum. From Fig. 2, it is readily apparent that the amplitudes of the speech vibrations delivered by the speaker's voice, in accordance with the present invention, are substantially increased with reference to the amplitudes of the normal speech, and with reference to amplitudes of the noise in the assumed ambient noise spectrum in which the speaker is immersed. In the latter connection it is apparent that amplitudes of the combined mechanical and natural speech vibrations of the speaker are substantially increased without affecting either his vocal efforts or the level of the ambient noise. It will be noted that the summation curve representing normal speech plus reinforced speech indicates a less favorable addition than arithmetic addition to take account of possible out-of-phase relation that may be present.

Referring to Fig. 1, the speaker may apply the speech delivered by his voice to a microphone 20 connected by a pair of leads 2i, 2! to asuitable public address system or the like, not shown, where both the speaker and microphone 20 are immersed in an ambient noise spectrum of. a high level. When the listener, at the remote end of the public address system, is immersed in ambient noise which has a level equal to or less than that in proximity of the speaker, such listener would obtain substantially the full benefit of the improved speech-to-nolse ratio produced at the microphone in accordance with the present invention as hereinbefore described.

a noise which has a level higher than that in proxi- A obtain benefit from the improved speech-to noise,

mity of the microphone, such listener would also ratio at the microphone in a manner that will now be explained. This is. accomplished by increasing the gain of the public address system to such value that the transmitted noise is reproduced at the listening location at a level. which is higher than that of the noise at the listening location. This means that, at the same time, the transmitted speech is also reproduced at the listening location at an increased level which maintains the speech-to-nolse ratio produced at the microphone as above mentioned. Should the transmitted speech be reproduced at a level too high for physical comfort, the listener may restore the reproduced speech to a comfortable level by employing ear defenders, or similar means, for attenuating both the speech and noise-in the ear canal before they reach the ear drum.

Referring to Figs. 1 and 3, the sound vibrations produced in accordance with Fig. i may be applied directly to the skin in the, region ,of the throat of the speaker as shown in Fig. 3, and thereby introduced' into the vocal cavities of the speaker. In this connection, it is understood the circuit portion shown to the left of the line XX in Fig 3 may be substituted for the circuit shown to the left of the line X-X in Fig. 1; and further the operation of Figs. 1 and 3 is substantially the same as that hereinbefore explained with reference to Fig. 1.

In Fig. 4 the harmonic currents supplied over the pair of leads I6, l6 are divided into three bands by the band-pass filters 25, 26 and 21, and

thereafter into three bands of corresponding sound vibrations by the electroacoustic converters 29, 30 and 3|, respectively. This serves to reduce the peak factors which tend to increase the required maximum excursion of'the diaphragm of the electroacoustic converter l7, Fig. 1.

In Figs. 1, 3 and 4, the microphone and associated public address system may be omitted so that the speech is directly transmitted through the air as the transmission medium from the speaker to the listener, where both the speaker and listener may be immersed in an ambient noise spectrum as 'hereinbefore mentioned. The arrangements'of Figs. 1, 3 and 4 minus the public address system operate substantially identically as described previously in connection with Figs. 1, 3 and 4 using the public address system.

What is claimed is:

1. In reinforcing'the amplitudes of speech vibrations produced in the vocal organism of a human and delivered by the human voice, including sound vibrations of fundamental and harmonic frequencies in the region of the skin of the v human throat after being naturally produced therein, the-methodwhich comprises translating the fundamental sound vibration picked up from the skin of the throat into a plurality of other sound vibrations extending over a certain audible frequency range corresponding at least in part to the frequency range ofthe vibrations produced in the throat but not including the fundamental vibration, and having amplitudes increasing with frequency over said part of said certain frequency range, and introducing 'said other sound vibrations into the vocal cavities of the human for molding into articulate sounds, together with the vibrations naturally produced in the human throat, whereby the amplitudes of the speech vibrations delivered by the human voice are substantially reinforced.

2. In reinforcing the amplitudes of speechvibrations produced in the vocal organism of a human .and delivered by' the human voice, in-

cluding sound vibrations of fundamental and ban monic frequencies in the region of the skin of the human throat after being naturally produced therein, the method which comprises translating said fundamental vibration picked up from the skin of the throat into a plurality of electrical currents havingfrequencies related harmonically to said fundamental vibration and extending over a certain range of audible frequencies, translating said harmonic currents. into "a plurality of sound vibrations whose energy is lower than normay speech energy at one end of the speech range but higher than normal speech energy at the 7 its amplitude to opposite end of the speech range, and introducing the latter sound vibrations into the human vocal cavities for molding into audible sounds, together with the vibrations naturally produced in the human throat, thereby substantially increasing the amplitudes of the speech vibrations delivered by the human voice.

3. The method of increasing the amplitudesof speech vibrations produced in the vocal organs of a human and delivered by the human voice, including sound vibrations of fundamental and harmonic frequencies at the skin in the vicinity of the human throat after being naturally produced therein, which method comprises picking up the sound vibrations from the human throat and translating them into an electric current of a fundamental frequencyv corresponding to that of said sound vibrations, translating said fundamental current into a plurality of harmonic currents whose frequencies extend over a certain audible frequency range corresponding at least in part to the frequency range of the vibrations produced in the throat but not including current of the fundamental frequency, preshaping the amplitudes of, said harmonic currents, converting the preshaped harmonic currents into sound vibrations, and introducing the latter sound vibrations into the vocal cavities of the human for molding into articulate sound, together with the speechvibrations naturally produced in the human throat, thereby substantially increasing the amplitudes of the speech vibra tions delivered by the human voice.

4. In speech transmission in ,noisy surroundings the method comprising picking up vocal energy from the talker with a high speech-tonoise. ratio compared with the ratio existing in noise of a predominant frequency characteristic,

the method comprising picking up vocal energy directly from the talkers vocal parts at a point where the speech-to-noise ratio is higher than in the surrounding up energy a sound wave in which'the ratio of high frequency level to .low frequency level is .much greater than in the case of normal speech, shaping said sound wave with respect to the noise frequency characteristic to increase the ratio of that of the noise, frequency for frequency, and introducing said shaped sound wave into the talkers vocal cavities to be molded by the talker's vocal parts into articulate speech.

6. In combination in apparatus for increasing.

the amplitudes of speech vibrations in the vocal organism ofa speaker and delivered by his voice, means for picking up the fundamental vibration from the speaker and translating it into a plu-" rality of sound vibrations having frequencies extending over all but the lower portion of the speech range and having amplitudes preshaped such that those or the higher frequencies are larger than-those of the lower frequencies and means for introducing the latter sound vibrations into the human vocal cavities for molding into portion of the band, relative to air, deriving from such picked- I articulate sound, together with vibrations produced. in the throat, whereby the amplitudes of the speech vibrations delivered by the human voice are substantially increased.

7. In combination-in apparatus for increasing the amplitudes of speech vibrations produced in the vocal organism of a talker immersed in an ambient noise spectrum and delivered ,by his voice-means for picking up vocal energy from they talker and translating it into a plurality of harmonic'currents, and means for translatin said harmonic currents into sound vibrations and for introducing the latter sound vibrations into the vocal cavities of the talker for molding into articulate sounds, together with the sound vibrations naturally producer-lv in his throat, so that the amplitudes of the speech vibrations emitted from the talkers lips are substantially increased with reference to the amplitudes of the frequencies in the ambient noise spectrum.

8. The combination according to claim 7 in I which said fundamental translating means inchides means for relatively varying the amplitudes of individual harmonic currents.

9. The combination according to claim '7 in which said harmonic current translating means comprises means for introducing the latter sound fundamental current to produce harmonic currents whose frequencies correspond at leastin produced in the throat, so as to reinforce the amplitudes of the speech vibrations delivered bythe human voice. i V

12. A system for'reinforcing the intensity of speech produced in the vocal organism of a vibrations into the vocal cavities of the talker through his mouth. a

10. The combination according to claim 7 in which said harmonic current translating means comprises means for introducing the latter sound vibrations into the vocal cavities of the talker through-the skin in the region of his throat;

11. In combination in apparatus for reinforcing the amplitudes of speech vibrations produced in a the vocal organism of a talker and delivered by his voice, including sound vibrations of fundamental and harmonic frequencies in the region of the skin of the talkers throat after being naturally produced therein, means for picking up the vibrations from the skin of the throat and speaker immersed inambient noise and delivered by his voice, comprising in sequence, means ap-, plied to the surface of the skin of the speaker's throat for picking up sound vibrations of fundamental and harmonic frequencies and translating them into speech currents including a current of fundamental frequency and currents harmonlcally related to said fundamental frequency,

means for selecting said fundamental current 1 and suppressing said harmonics thereof, means for amplifying said fundamental current, means for utilizing said amplified fundamental current to produce further harmonic currents, means for selecting said further harmonic currents and suppressing said fundamental current, means for relatively varying the amplitudes of individual further harmonic currents, and means for translating the varied harmonic currents into sound vibrations, and for introducing the latter sound vibrations into the vocal cavities of the speaker for molding intoarticulate sounds, together with the vibrations naturally produced in the speaker's translating them into an electric current of a fundamental frequency, means for utilizing said throat, and therebysubstantially reinforcing the amplitudes of the speech vibrations delivered by the human voice, with reference to the ambient noise spectrum. s 1

NORMAN R. FRENCH.

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